Cold accumulating material and method of manufacturing the same

Abstract

The extremely low temperature cold accumulating material for use in refrigerators, for example, comprises particles containing at least one kind of rare earth element selected from a group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. The proportion of particles each having a particle size of 0.01 to 3 mm is 70% or greater by weight with respect to the whole particles and the proportion of particles each having a shape such that the ratio of the major diameter to the minor diameter is not greater than 5 is 70% or greater by weight with respect to the whole particles. The particles are manufactured by quenching and solidifying a molten metal containing at least one kind of rear earth element described above. The thus manufacured extremely low temperature cold accumulating material is improved in cold accumulating efficiency and is specifically improved in mechanical strength and in chemical stability.

What is claimed is: 
     
       1. A cold accumulating material, comprising: a set of particles having a total weight and a particle size of 0.01 to 3 mm, wherein each particle contains at least one kind of rare earth element selected from a group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and surface roughness of said particles is not greater than 10 μm in terms of a maximum height R max .   
     
     
       2. A cold accumulating material according to claim 1, wherein the surface roughness of said particles is not greater than 5 μm in terms of the maximum height R max . 
     
     
       3. A cold accumulating material according to claim 1, wherein an average crystal grain size of the particles is 0.5 mm or smaller. 
     
     
       4. A cold accumulating material according to claim 1, wherein at least a part of an alloy structure of said particles is formed of an amorphous phase. 
     
     
       5. A cold accumulating material according to claim 1, wherein the proportion of particles having small defects having a length of 10 μm or longer is 30% or smaller by weight relative to the total weight of said particles. 
     
     
       6. A cold accumulating material according to claim 1, wherein the content of each of impurities including O, N, Al, Si and H contained in said particles is 2000 ppm or less.